Various techniques for monitoring machinery are known in the art. Some methods, such as described, for example, in PCT publication WO 01/71362 or U.S. Pat. No. 6,694,285 to Choe, are based on measurement of mechanical vibrations.
Other methods are based on sensing of acoustic signals from the machinery. These methods do not require physical coupling of sensors to monitored machinery.
US patent publication 2016/0117905 to Powley, describes comparing environment sounds to predetermined signatures to identify events occurring in the environment.
U.S. Pat. No. 6,507,790 to Radomski, titled “Acoustic Monitor”, describes monitoring the sound from rotating or non-rotating machinery and comparing the monitored sounds to those collected in a learn mode.
U.S. Pat. No. 8,903,558 to Jarrell et al., titled Monitoring Pipeline Integrity, describes the use of a microphone to sense acoustic sound signals from a monitored pipeline. The sensed signals are compared to previously acquired baseline signals to detect threat conditions.
U.S. Pat. No. 8,607,093 to DeHaan et al., titled “Systems and methods for detecting machine faults in network using acoustic monitoring”, describes detecting machine faults in a network using acoustic monitoring. Acoustic data from near a subject machine is analyzed using spectral analysis. Monitored acoustic data is compared to acoustic profiles of malfunction components or other anomalous conditions. One example given by DeHaan relates to identification of a bearing whine of a failed hard disk.
US patent publication 2002/0020561 to Alft et al., titled “Real-time control system and method for controlling an underground boring machine”, describes comparing signals from a boring machine to an acoustic profile of the machine developed empirically.
European patent application 3 015 866 to ABB Technology AG, titled: “A method of automatic determination of rotational speed of a shaft in a rotating machine”, describes generating a tone of known frequency in proximity to a shaft, recording acoustic signals responsive to the generated tone and accordingly determining a speed of the shaft.
In many cases, acoustic signals suffer from high levels of noise which may interfere with comparison of acoustic signals.
U.S. Pat. No. 6,778,894 to Beck et al. describes monitoring acoustic noise signal collected by a microphone from a working vehicle. This patent suggests determining a parameter from the signal, in particular the frequency and/or amplitude of vibration.